1. Field of the Invention
The present invention relates to a mobile communication system and an MBMS service relevant information transfer method for use therewith, and more particularly to a multicast service MBMS (Multimedia Broadcast Multicast Service) for use with the mobile communication system.
2. Description of the Prior Art
Multicast in the mobile communication system is referred to as MBMS, and has a function of distributing the same contents data to the radio terminals (UE: User Equipment) existing in a cell.
Radio Network Controller (RNC) with the MBMS function finds the number of radio terminals (UE: User Equipment) existing in a cell and joining an MBMS service to receive the contents data and determines whether the contents data is transferred to each radio terminal in the cell with a PtP (Point to Point) method or a PtM (Point to Multipoint) method.
That is, if the number of radio terminals is greater than a threshold preset in the Radio Network Controller, the contents data is transferred with the PtM method, or conversely, if the number of radio terminals is smaller than the threshold, the contents data is transferred with the PtP method.
When the contents data is transferred with the PtP method, it is meant that the contents data is transferred on a wireless dedicated channel, and when the contents data is transferred with the PtM method, it is meant that the contents data is transferred on a wireless common channel. Whether the contents data is transferred with the PtP method or PtM method is determined depending on the number of radio terminals, taking into consideration to save the radio transmission power.
A method of the Radio Network Controller to find the number of radio terminals in the cell involves transmitting an MBMS Notification message and counting the number of radio terminals responding to the MBMS Notification message (e.g., refer to Non-Patent Document 1).
An MBMS control process of the Radio Network Controller will be described below. FIGS. 4 and 5 are context information stored within the memory of the Radio Network Controller. The context information of FIG. 4 is called “UE Context”, and the context information of FIG. 5 is called “MBMS Service Context”.
The “UE Context” of FIG. 4 stores the information for the Radio Network Controller to control the radio terminal when the radio terminal performs the normal communication (voice communication or packet communication), including IMSI (International Mobile Subscriber Identity: fixed identifier for radio terminal), RRC (Radio Resource Control) State, RAB (Radio Access Bearer) Info, and positional information (cell information in which the radio terminal is located). This “UE Context” is generated by the Radio Network Controller, when the radio terminal starts to perform the normal communication (voice communication or packet communication) with the network.
The “MBMS Service Context” of FIG. 5, given for each MBMS service, stores the information for the Radio Network Controller to control the MSMB service, including IP (Internet Protocol) Multicast Address (IP address of a server sending out the contents data of MBMS service), APN (Access Point Name: GGSN (Gateway GPRS (General Packet Radio Service) Support Node) in this embodiment), MBMS service ID (MBMS service identifier), MBMS RAB Info (RAB information for transferring the contents data of MBMS service) and the IMSI of the radio terminal having joined the MBMS service for each cell.
The Radio Network Controller generates this “MBMS Service Context” when receiving a Session Start Message from the SGSN (Service GPRS Support Node) (see e1 to e11 in FIG. 10). Besides, the Radio Network Controller generates the “MBMS Service Context” when starting the normal communication (voice communication or packet communication) after the radio terminal joins the MBMS service. At this time, the Radio Network Controller also generates the “MBMS UE Context Info” as shown in FIG. 4 and stores it in the “UE Context”.
If the Radio Network Controller generates the “MBMS Service Context” when starting the normal communication (voice communication or packet communication) after the radio terminal joins the MBMS service, the Radio Network Controller can find the number of radio terminals having joined the MBMS service at the later time when receiving a Session Start message from the SGSN, and determine whether the contents data of MBMS service is transferred with the PtP method or PtM method.
The Radio Network Controller transmits an MBMS Notification message on the wireless common channel, after receiving the Session Start message, to notify that the contents data of MBMS service starts to be transferred soon.
Also, the radio terminal may not be able to receive the MBMS Notification message transmitted on the wireless common channel, depending on its state. For example, the radio terminal is unreceivable on the wireless common channel while communicating on the dedicated channel. In this case, the Radio Network Controller, seeing an RRC State in the “UE Context” of FIG. 4, transmits the MBMS Notification message to the radio terminal on the dedicated channel and informs that the contents data of MBMS service is transferred soon, if the radio terminal is in a state not capable of receiving the MBMS Notification message on the wireless common channel (e.g., a state where it is communicating on the dedicated channel).
The Radio Network Controller managing the radio terminals in communication with the network is referred to as a serving Radio Network Controller (Serving RNC) and manages the movement of radio terminals with the “UE Context”.
When the radio terminal moves from an area of the Serving RNC to an area of the Radio Network Controller adjacent to it, the serving Radio Network Controller performs the Relocation to pass a management right of the radio terminal to the Radio Network Controller of movement destination for the line utilization efficiency.
The serving Radio Network Controller becomes the Radio Network Controller of relocation source during execution of a relocation procedure. This Radio Network Controller of relocation source is referred to as a source Radio Network Controller (Source RNC), and the Radio Network Controller of relocation destination is referred to as a target Radio Network Controller (Target RNC).
When the relocation is performed, according to the present system specifications, the relevant information (“MBMS UE Context Info” in FIG. 4) of an MBMS service joined by the radio terminal is not notified from the source Radio Network Controller to the target Radio Network Controller of relocation destination, although the radio terminal joins the MBMS service.
Specifically, in FIGS. 2, 3 and 11, it is supposed that the radio terminal joins a certain MBMS service while communicating with the network in the area of the source Radio Network Controller (in the state of FIG. 2). The source Radio Network Controller stores the relevant information of the MBMS service joined by the radio terminal in memory (generates the “MBMS UE Context” of FIG. 4) in a procedure in which the radio terminal joins the MBMS service (f1 in FIG. 11). The reason of storing the relevant information in memory is to determine whether the PtP method or PtM method is employed.
The radio terminal moves from the area of the source Radio Network Controller to the area of the target Radio Network Controller, and the source Radio Network Controller decides to perform the relocation procedure (f2 in FIG. 11).
The source Radio Network Controller transmits a Relocation Required message to the SGSN (f3 in FIG. 11), and the SGSN transmits a Relocation Request message to the target Radio Network Controller (f4 in FIG. 11). At this time, the relevant information of the MBMS service joined by the radio terminal is not transferred to the target Radio Network Controller in accordance with the conventional specifications.
Since the relevant information of the MBMS service joined by the radio terminal is not transferred, the “MBMS UE Context Info” does not exist in the “UE Context” (see FIG. 4) at the target Radio Network Controller, and the IMSI of the radio terminal is not stored in the “MBMS Service Context” (see FIG. 5) (f5 to f13 in FIG. 11).
[Non-Patent Document 1] “Multimedia Broadcast Multicast Service” (3GPP TS23.246 version 6.0.0 2003-09).